(1) Field of the Invention
The present invention relates to the capacitor input type constant voltage circuit and the switching power supply unit using said constant voltage circuit. Also, the present invention relates to the stabilized power supply unit for half wave rectifying the AC input power respectively in both positive and negative sides and then reinverting said DC into the AC.
(2) Description of the Prior Art
Generally, the capacitor input type full-wave rectification circuit is designed as shown in FIG. 1.
The AC power supply 10 is rectified by the bridge type full wave rectification circuit 11 and smoothed by the capacitor 19 for being the DC voltage to be supplied with the load 6, such as the switching power supply.
In the circuit of described above, the rectification voltage inputted into the capacitor 19 generates the sine full waveform as shown in FIG. 2(a). Said voltage creates the ripple voltage waveform when smoothed by the capaciter 19. The current inputted into said capacitor 19 flows only when the voltage of the capacitor 19 is lowered. The waveform of said current comprises narrow duty cycle, high peak and the peak value as shown in FIG. 2(b), though the waveform of the input voltage is the sine wave. Thus, the power factor of said current remains as low as 0.5.
T he power factor improvement circuit has been used conventionally for solving the problems as described above.
In the DC constant voltage circuit comprising the boosting chopper circuit 31 shown in FIG. 3, the PWM controlling IC 48 for the power factor improvement is conventionally used as the IC for constant voltage and power factor improvement. The detailed explanation of said IC 48 is shown in FIG. 4.
A DETAILED EXPLANATION IS
In FIG. 3, the AC power supply 10 is connected to the input side of the full wave rectifier 11, the boosting chopper circuit 31, the capaciter 29 and the load 6 are connected to the output side of said rectifier 11. The boosting chopper circuit 31 comprises inductor 23, diode 27, switching element(such as MOSFET) 25, capaciter 29 and said IC 48.
The +output side of said rectifier 11 is connected to No.6 pin of said IC 48 through the resistor 49 and connected to No. 8 pin through the integration circuit 5. The integration circuit 5 comprises resistor 50 and capaciter 53..
Resistor 4 is inserted into the -output side of said rectifier 11, the rectifier 11 side of said resistor 4 is connected to No.5 pin and the +side of said capaciter 29 is connected with No.11 pin. No.16 pin which is the PWM output terminal of said IC 48 is connected to the gate of said switching element 25.
The power factor improvement is made possible by creating a waveform of input current similar to that of input voltage.
In the circuit in FIG. 3, the waveform of input voltage is detected, as signals required for improving the power factor, by resistor 49, the effective input voltage by the integration circuit 5, the waveform of the input current by resistor 4 and the output voltage by capaciter 29 respectively. The power factor is made possible when these signals are inputted into and controlled at the same time No. 6 pin, No. 8 pin, No. 5 pin and No. 11 pin respectively.
The prior art for improving power factor with said IC 48 is controlled complicately and has to connect a large number of parts around said IC 48, so there has been the problem such that the circuit is designed complicately and to be expensive costs.
The applicant has already filed the stabilized power supply unit of the AC constant voltage in which one side of the AC input terminal and one side of output terminal are connected as a common line, as shown in FIG. 6 (U.S. Pat. No. 4,823,247).
In FIG. 6, the voltage Vi of the AC power supply 10 as shown in FIG. 7(b) is applied between the AC input terminals 2 and 3. The AC voltage is half wave rectified at both positive and negative sides of voltage multiplication rectifier and smoothed by capaciters 19 and 20 to obtain DC voltages +V1 and -V2. Said +V1 and -V2 are equal on the positive side (described with the solid line) and negative side (described with the dotted line) with respect to the common line 16 (shown in FIG. 7(b). The voltages +V1 and -V2 are chopped by the transistors 25 and 26 of the boosting chopper circuits 31 and 32 to obtain +V3 and -V4 which are higher than +V1 and -V2 at both ends of the capaciters 25 and 26 (as shown in FIG. 7(d)).
In this FIG. 7(d), the period t=1/f(f.gtoreq.20 k/Hz) and the areas m and n marked are equal (t1=ON -time of the transistor 25). In other words, the controlling circuits 43 and 44 detect +V3 and -V4 when they increased, control so that reduce ON time t1 of the transistors 25 and 26 be with drive circuits 41 and 42, whereas said circuits 43 and 44 control to increase said ON time t1 when +V3 and -V4 lower.
The pulse voltage shown in FIG. 7(d) is smoothed by the rectifiers 27 and 2B and the capaciters 29 and 30 to be transmitted to DC AC inverter 37. Transistors 33 and 34 of said DC-AC inverter 37 become ON and OFF alternatively and the ON time and OFF time correspond the AC output waveform respectively to produce the pulse voltage waveform V5 (as described with the solid line in FIG. 7(e)). This V5 after harmonic wave component through filter circuit 96 which is composed of inductor 35 and capaciter 36, becomes AC output voltage V0 (as described with the dotted line in FIG. 7(d)).
When the AC voltage input is interrupted due to power, DC voltages of the batteries 38a and 38b are transmitted to boosting chopper circuits 31 and 32 respectively through diodes 39 and 40. The actions after boosting chopper circuits 31 and 32 are the same as previously explained.
DC output voltage settings of batteries 38a and 38b are to be slightly lower than said +V1 and -V2.
When the excessive load current flows due to unexpected causes, load current detection circuit 13 and the output voltage detection circuit 12 detect such are current, switch the contactor of change over circuit 14 to the direct supply line 1 side, AC power directly to load 6 through AC input terminal 2 and direct supply line 1. In this case, the other input terminal and output terminal 9 are connected by a common line 16, and there is no problem.
Batteries 38a and 38b are charged when the AC voltage is inputted by the charging circuit which is not shown.
The problem concerning the circuit shown in FIG. 6 is explained by using block diagram 5. In FIG. 5, the voltage rectified by diodes 17 and 18 of voltage multiplication rectifier 21 is the half wave rectification and voltage smoothed by capaciters 19 and 20 is DC voltage coupled with commercial ripple voltages (with solid and dotted lines in FIG. 7(b)).
However, the current inputted into capaciters 19 and 20 flows only when voltages of said capaciters 19 and 20 lower. This current generates waveforms comprising the nallow duty cycle, high peak and high peak value, though input voltage is sine wave. Thus, power factor becomes around 0.5. In the AC constant voltage circuit comprising common line 16 connecting AC input terminal 3 and output terminal 9, positive and negative boosting chopper circuits 31 and 32 boosting and chopping DC voltage of half rectificated respectively in each positive and negative sides and the DC-AC inverter 37 inverting said DC voltages into the AC, there has not been the circuit improved power factor in the prior art.
In DC constant voltage circuit with rectifier 11 and boosting chopper circuit 31 which is controlled by general purpose PWM control IC 48, as shown in FIG. 1 through FIG. 4, power factor has been obtained by said IC 48 which is used exclusively for the power factor improvement.